The present invention relates to a circuit and method for generating and error voltage onto a direct current voltage and, more particularly, to generating a digitally controlled error voltage for incrementally changing a direct current reference voltage in a regulator system.
In alternator regulators in particular and many other general applications, it is required to generate a small error voltage which floats on a much larger direct current voltage component. For example, in a switch mode operated voltage regulator system the system output may be either switched on or off depending on the level of an error voltage generated within the system. One problem which may be faced is how to generate a small error voltage on top of a relative large direct current reference voltage. One method that might be used is to use a plurality of resistors across which the reference voltage is developed. By incrementally changing the resistance values a particular error voltage could be generated that floats on the larger direct current voltage component. However, this technique requires large magnitude resistors and is therefore not suitable for use in an integrated circuit system.
Thus, a need exists for a circuit and method to generate a small incrementally varying error voltage onto a floating reference voltage which circuit is suited for manufacture in integrated circuit form.